...It does not mean the author must give you such code for free. It means when you have the code, you are free to distribute it (or modify) under the same license. You can distribute it however you like - for free or for money.

...But you can do something like commercial render engines do: the export plugin is GNU (uses Blender API) and converts scene data to commercial application (ie. renderer) which is not GNU (doesn't use Blender API) and the licenses differ. This works because the addon is not dependent on the non-GNU application.

...But you can do something like commercial render engines do: the export plugin is GNU (uses Blender API) and converts scene data to commercial application (ie. renderer) which is not GNU (doesn't use Blender API) and the licenses differ. This works because the addon is not dependent on the non-GNU application.

Right this is indeed what Octane for Blender is doing,the GPL part is Blender OctaneRender™ edition (Blender with OctaneRender RenderServer support integrated), so the modified blender source code should be accessible to anyone*,while OctaneRender Server is the actual renderer with Otoy non GPL source code so obviously non-public.